1. Field of the Invention
This invention relates to an image transforming apparatus (image effect apparatus) for displaying a realistic object etc. by mapping the image information, processed by special effect processing, on an effect surface which is a surface of the image information mapped on an externally defined three-dimensional surface and which is changed in accordance with the information instructing changes in its shape, and by depicting illumination in the manner of taking account of the relation between a light source and a line of sight. It also relates to an image transforming method (image effect processing method) comprising mapping the image information, processed by special effect processing, on an effect surface which is an externally defined three-dimensional surface and which is changed in accordance with the information instructing changes in its shape and by depicting illumination in the manner of taking account of the relation between a light source and a line of sight.
2. Description of the Related Art
There are a variety of methods in the prior art for producing visual effects by taking account of illumination effects. An example of a technique of realistically displaying an object in, for example, computer graphics is shading an object surface. This technique resides in displaying a surface perpendicular to the light beam with utmost brightness and displaying a surface with less brightness as the surface is removed from the perpendicular direction. There is also known a so-called texture mapping, that is, displaying detailed visual information of an object surface or a model of the material quality reproducing the properties of an effect surface.
There has also been used a so-called light tracking method consisting in accurately locating by which route a light beam emanating from a light source is reflected, transmitted or absorbed by an object before ultimately reaching an eye or a pixel and constituting pixels based on the resulting information. The image displayed in accordance with the light tracking method is highly realistic because the method depends on actual calculation of the intensity of reflection of the incident light corresponding to reflectance of a reflecting object as well as the scattering direction of the incident light.
If the light from a light source, such as the sun, is radiated on an effect surface, which is a three-dimensional surface on which the image information processed with special effect processing is mapped, the surface perpendicular to the light is displayed most lightly, while the intensity of reflection is gradually lowered towards an outer periphery, that is, with increasing deviation from the perpendicular direction. If the shape of the effect surface is changed to a cylinder as shown in FIG. 1e, since the portion of the surface perpendicular to the light is parallel to the axis of the cylinder, the light surface perpendicular to the light is displayed as a stripe the size of which is obtained by calculation.
There is also known a method consisting in applying the light only to a predetermined portion of a Z-coordinate in a three-dimensional address space to improve the effect of illumination.
It is noted that, although the image in which the effect of illumination based on the light tracking method is taken into consideration is highly true to the real object, mathematical processing for generating an image is complicated so that extensive calculation is required for image generation. Consequently, in a small-sized system, real-time image data generation is difficult to achieve because of the lower processing speed even if calculation is carried out in accordance with the above-described system to display the image. On the other hand, a realistic image effect cannot be produced by the apparatus which resorts to the above-mentioned simplified method. In view of the above-mentioned problem of the prior art, the present Applicant has already proposed a special effect device in an inexpensive digital effect device in which an image displayed on an effect surface is depicted with realistic effects of illumination by fixing the relation between the incident light and the effect surface.
However, since the relation between the incident light and the effect surface are fixed, there is room for improvement in connection with continuous transition from a plane surface to a curved surface. Consequently, if attempts should be made for mapping the image information on the effect surface which has been moved and rotated arbitrarily, a further improvement is desired to produce a realistic image in which the effects of illumination are exhibited satisfactorily.